State of the art chargers (e.g., chargers for mobile battery-powered devices) include a variety of feedback loops in order to guarantee their performance under specified operating conditions. One of these feedback loops monitors the input voltage (supply voltage, bus voltage). Cable resistance and source output resistance determine the input voltage to the charger at a given input current. If the charger draws too much current, the input voltage of the charger may drop and, in worst case, cause system faults. In order to prevent drop of the input voltage beyond a certain threshold, the input voltage may be monitored and the input current may be controlled accordingly, for example by controlling the current (output current) that is output by the charger.
Examples of chargers may include a switching DC-DC converter circuit, such as a buck converter. The buck converter may be controlled by a feedback loop that is commonly referred to as analog buck current control (ABCC) loop. In this loop, the input voltage is compared to a reference voltage, for example by means of an operational transconductance amplifier (OTA), and an error voltage for controlling the buck converter is generated on the basis of a result of the comparison. The error voltage may be generated by passing an output of the OTA through a compensation network that may serve to compensate a frequency response of the loop. In such charger, the DC loop gain of the ABCC loop would be given by
                              L                      D            ⁢                                                  ⁢            C                          =                              -                          [                              R                cab                            ]                                ⁢                                                    A                                  ABCC                  OTA                                            ⁢                              G                                  m                  buck                                                                    1              +                              s                ⁢                                                                  ⁢                                  τ                  2                                                                                        [        1        ]            where Rcab represents the cable resistance, AABCCOTA is the voltage gain of the OTA (including loading by the compensation network), Gmbuck is the buck transconductance transfer function, and τ2 is the dominant time constant of the ABCC loop. As can be seen from equation [1], the DC loop gain LDC is directly dependent on the cable resistance Rcab. The cable resistance Rcab can vary from a few milliohm (in test bench scenarios) to a few ohms (typically one to two ohms, but in the worst case even more, for example due to faulty cables or bad connectors, etc.).
As a result, in state of the art techniques, also the cross-over frequency of the loop changes directly with the cable resistance Rcab and the DC gain LDC is low for low cable resistance Rcab.
All the above facts significantly impede appropriate regulation of the input voltage of the charger.